docs: def extract_forward_and_reverse_complement(
              self, forward_reads_to_extract, reverse_reads_to_extract, database_fasta_file,
              output_file):
          '''As per extract except also reverse complement the sequences.'''
          self.extract(forward_reads_to_extract, database_fasta_file, output_file)
          cmd_rev = "fxtract -XH -f /dev/stdin '%s'" % database_fasta_file
  
          output = extern.run(cmd_rev, stdin='\n'.join(reverse_reads_to_extract))
  
          with open(output_file, 'a') as f:
              for record in SeqIO.parse(StringIO(output), 'fasta'):
                  record.seq = record.reverse_complement().seq
                  SeqIO.write(record, f, 'fasta')